Publication EP 1 075 928 describes a rigid core of the type to which the invention relates, which acts as a support for an unfinished tire from the start to the end of its manufacture. This core is made up of multiple segments which are independent of each other so that the core can be extracted in segments from the inside of a tire via the space available between the beads. This core is then put back together again to act as the support for the subsequent manufacture of another tire. A means is used to keep the segments assembled during the manufacture of the tire. Other, earlier publications also describe cores of the same type such as the publication U.S. Pat. Nos. 1,392,347 and 1,328,676, or more recently the publication EP 242 840.
Such a core must withstand numerous cycles of assembly and disassembly and must be extremely robust in order to guarantee a high level of geometrical quality as well as maintaining these qualities for an extended period of time despite the numerous cycles it is put through. Moreover, this core, when used as a means of moulding the inside part of the tire, must withstand high compressive forces. Its mechanical structure is therefore suitable for this type of use, which distinguishes it particularly from conventional supports used for tire manufacture as described for example in the publication U.S. Pat. No. 3,932,256.
In general terms, the core comprises a plurality of circumferentially adjacent segments located side by side in contact with each other via their transverse faces. The transverse faces of at least one segment converge away from the core in order to allow said core to be disassembled by removing this segment radially towards the interior. In practice the core comprises two kinds of segments: divergent segments, whose transverse faces are divergent radially outwards from the core, and so-called reverse segments, whose transverse faces are convergent outwards from the core.
Once assembled, the outer surface of the core constitutes the receiving surface, whose shape is essentially toroidal, and on which the profiled rubbery products are deposited to create the unfinished tire.
It is also known practice to deposit these rubbery products in the form of bands wound circumferentially in a spiral around the manufacturing form. The transverse profile of the bands and the pitch of the spiral define, in a known manner, the cross section of the product which it is wished to deposit at a precise location of the unfinished tire.
As a general rule, therefore, the first product deposited on the manufacturing form defines the inside surface of the tire. It is formed by a winding of contiguous bands made of a material which, once fully cured, is virtually impermeable to air.
The application by winding of the inner band of rubber is performed by a means capable of delivering the band either directly onto the surface of the manufacturing form using a nozzle for example, or from an extrusion station, so that the bands are deposited while still hot, before undergoing a consequent cooling phase. As a result of this, the product is more sensitive to deformations than a colder and stiffer product. In both cases the band is deposited directly on the surface of the receiving manufacturing form either by the extrusion nozzle or using an application means such as a wheel.
Whatever means is used, it has been observed that the first band deposited on the manufacturing form, i.e. the band in direct contact with the manufacturing form, sometimes breaks unexpectedly. These random breakages of the band are disruptive, in that they interrupt the winding cycle and cause substantial loss of time in reconfiguring the station, especially when the application cycle is controlled by automatic means.